A major disadvantage of prior art fast room temperature curing epoxies, i.e., mercaptan cured, is that the rapid gelation retards the development of full properties through the restriction of molecular motion and the cure mechanism involved. Extremely fast cures result in overly plasticized product due to the need to use a high level of curative. In addition, for epoxies cured by conventional amine or mercaptan curing agents, there is a critical mix ratio or stoichiometry for the resin/hardener mixture with thorough mixing necessary to achieve full cure.
In U.S. Pat. No. 4,092,296 a catalyst system for room temperature curing of epoxy resins is described which comprises a metallic fluroborate salt such as the tin, copper, zinc, nickel, lead or silver salt.
In U.S Pat. No. 4,396,754 there are described compositions of epoxy compounds and catalysts selected from lithium or group II metal salts of non-nucleophilic acids such as LiBF.sub.4, Ca(BF4).sub.2, Mg(BF4).sub.2, LiPF.sub.6, LiSbF.sub.6, LiAsF.sub.6, etc. Some of these compositions are reported to give very rapid cure at room temperature.
High temperature rapid curing epoxy resin systems are available utilizing high temperature or radiation curing. In these cases cationic ring opening polymerization of the epoxy rather than addition polymerization is achieved.
Suitable photoinitiators are diaryliodonium, diarylsulfonium, dialkylphenarylsulfonium, dialkylphenarylsulfonium, dialkyl4-hydroxyphenylsulfonium, triarylselenonium salts and related materials described in such patents as U.S. Pat. Nos. 4,069,054; 4,069,055; 4,138,255; 4,175,972; 4,175,973; 4,367,261; 4,374,066; 4,398,014; 4,399,071; 4,417,061, etc.
High temperature catalysts commonly employed are Lewis acid amine complexes such as Boron trifluoride monoethylamine which dissociate at elevated temperatures releasing the Lewis acid catalyst BF.sub.3. BF.sub.3 amine complex initiation of epoxies is reported to be described in U.S. Pat. No. 2,717,285.
While BF.sub.3 amine complexes are available which dissociate at room temperature, e.g., BF.sub.3 N-diphenylamine, room temperature curing using stable carbenium ions has not been commercialized.
Kinetic studies of trityl salt initiated polymerization of 1,2-butylene oxide in solution are reported in J. Polymer Sci: Polymer Chem Ed, 11, 1825-1839 (1973) and 14, 2853-2866 (1976). The polymers produced were low molecular weight oligomers which would not be useful as cured adhesives. Storage stable dispersions of trityl salts as initiators for curing epoxy resins to high molecular weight solids are not suggested.
Mechanistic studies of trityl and tropylium salt initiated polymerization of alkyl vinyl ethers, tetrahydrofuran and N-vinylcarbazole are reported by A. Ledwith in ACS Advanced Chem. Ser., 91 317-334 (1969).